Two scenarios have been proposed for interaction between the
groups exploiting the várzea, of white-water rivers and those
occupying the terra firme drained by black- and clear-water
rivers. One envisions the várzea, as a region of constant
population increase, creating demographic pressure that was
relieved by expansion up the principal tributaries (Lathrap,
1970: 74-7). The other views the várzea, as prime agricultural
land coveted by occupants of the terra firme.

Examining the affiliations of the phases identified thus far
along the Madeira, Tocantins, and Xingu reveals a sharp boundary
coincident with the first rapid on each river. Phases below this
point are affiliated with the Polychrome Tradition and those
above it belong to traditions restricted to the terra firme. This
segregation is particularly clear on the Tocantins (fig. 4.4) and
on the lower Xingu, where sites above and below the barrier are
in close proximity. Expansions of the Polychrome Tradition up the
Negro and the Solimões are late and seem attributable to the
advent of the Incised and Punctate Tradition rather than to local
population increase.

These distributions are compatible with environmental evidence
that the várzea and terra firme habitats are distinct and
require different specialized knowledge and procedures for
effective utilization, such that groups adapted to either are ill
equipped to exploit the other. A case can be made that the terra
firme was a more stable environment than the várzea, which was
subject to drastic fluctuations in subsistence productivity
because of unpredictable variations in the rate, timing, and
extent of annual inundation (Irion, 1984; Meggers, 1971: 146).

It is generally accepted that Amazonia experienced episodes of
climatic fluctuation during and since the Pleistocene, but until
recently evidence for their impacts on humans was restricted to
the disjunct distributions of languages and cultural traits
(Meggers, 1987). The existence of detailed relative chronologies
and numerous carbon-14 dates throughout the lowlands now makes it
possible to correlate local cultural discontinuities with
environmental oscillations.

When humans entered South America toward the end of the
Pleistocene, some 12,000-14,000 years ago, the lowlands were less
densely forested than at present. Although details are unclear,
it seems likely that the savannas of Roraima and northern Pará
are relicts of a corridor of relatively open vegetation that
extended from Venezuela to eastern Brazil (Barbosa, 1992). The
availability of similar kinds of resources across the basin would
have facilitated movement by hunter-gatherers and carbon-14 dates
indicate they had reached the south-eastern margin of the
lowlands by 11,000 BP (Schmitz, 1987, table II). The only
evidence thus far for their presence in the central Amazon takes
the form of rare stone projectile points (Simões, 1976) and
early carbon-14 dates from the lower levels of ceramic sites,
which may represent campfires of pre-ceramic occupants of the
same locations. The oldest result is 7320 ± 100 BP (SI-4277)
from a tributary of the middle Madeira.

The vegetation assumed its current composition and extent
during subsequent millennia, but the process was disrupted by
several widespread episodes of climatic fluctuation. Pollen
records from marginal locations indicate that prior to the
Christian era savanna replaced forest during several centuries
and briefer episodes occurred about 1,500, 1,200, 700, and 400
years ago (Absy, 1982; Van der Hammen, 1982). These episodes
coincide with cultural replacements in welldated archaeological
sequences throughout the lowlands.

Oscillations reflected in a pollen profile from Lago Ararí on
eastern Marajó correlate with successive archaeological phases
in the surrounding region (fig. 4.11). The Ananatuba Phase, the
earliest pottery-making group on the island, arrived when forest
vegetation was dominant. By 2590 i 100 BP (Beta-2289), forest
pollen had declined from 65 per cent to 30 per cent, implying
significant alteration in the climate and biota (Absy, 1985, fig.
4.9). The terminal date for the Mangueiras Phase probably marks
the point during the transition at which declining subsistence
resources could no longer sustain sedentary communities. The
inception of the Formiga Phase coincides with re-expansion of the
forest about 2000 BP. The arrival of the Marajoara Phase follows
the shorter period of aridity about 1500 BP and its termination
coincides with the 700 BP episode.

Similar cultural discontinuities are evident in all the
regions where local sequences are sufficiently complete and well
dated to minimize the probability of sampling error. With rare
exceptions, the initial ceramic complexes throughout the lowlands
postdate 2000 BP (fig. 4.12). On the Llanos de Moxos in
north-eastern Bolivia, most phases begin or end about 1500, 1000,
and 700 BP. In the Silves-Uatumã region on the left bank of the
middle Amazon, replacements take place about 1,500, 1,100, 800,
and 400 BP. On the lower Xingu, transitions occur about 1,500,
1,100, 800, and 400 BP. The only significant disagreement between
the timing of climatic changes inferred from pollen profiles and
the cultural replacements is the clustering of the latter about
1000 BP rather than 1200 BP. This may reflect more precise dating
for the archaeological sequences. Droughts too brief to leave a
pollen record are more frequent (Meggers, 1994; Sternberg, 1987:
206; Stockton, 1990) and failure to incorporate their effects
places unwise schemes for "development" in greater
jeopardy.

The contemporaneity of climatic fluctuations and cultural
discontinuities implies a cause and effect relationship. Evidence
that many plants respond to variations in rainfall by failing to
flower and fruit indicates that the cause was deterioration of
local subsistence resources below the requirements of small
semi-sedentary communities (Leigh et al., 1982). The effect may
have been emigration, decimation, adoption of a wandering way of
life, or a combination of solutions. Although emigration cannot
yet be traced archaeologically, it is implied by the disjunct
distributions of the principal Amazonian languages as well as by
the different ceramic affiliations of successive phases in the
archaeological sequences.

From the perspective of temperate-zone observers, the failure
of indigenous inhabitants of Amazonia to equal the population
density and sociopolitical complexity achieved in the adjacent
Andean region signifies cultural stagnation. From the perspective
of the tropical environment, however, their way of life
represents highly successful exploitation of unpromising and
unpredictable resources. Wild plants and animals are solitary and
dispersed, agricultural intensification is precluded, and food
cannot be stored for future consumption (Bergman, 1980: 109-10;
Good, 1989: 78). The number, variety, and ingenuity of the
cultural practices that have developed for manipulating
environmental constraints, inhibiting overexploitation, and
optimizing the productivity of this complex ecosystem are no less
remarkable than the intricate interactions among the climate,
soils, and biota.

Comprehensive knowledge of the flora provides alternatives
when primary resources fail (Berlin, 1984: 32; Boom, 1989: 82-3;
Carneiro, 1978; Cavalcante and Frikel, 1973: 5). The Yanomami are
reported to experiment continuously with new plants they
encounter (Fuentes, 1980: 23). The abundance of useful species is
enhanced by selective cutting and weeding and by transplanting
(Irvine, 1989). Multiple varieties of the principal cultigens
with differing tolerances for disease, moisture, soil, and other
variables are usually planted to minimize loss (Baster, 1987:
412; Johnson, 1983: 44-5). Knowledge of the fauna is equally
detailed and includes many species not ordinarily consumed
(Berlin and Berlin, 1983: 320-2).

Prenatal and postnatal practices offsetting population
increase are numerous and varied (Meggers, 1971: 103-10), and
include prolonged lactation, contraception, abortion,
infanticide, abstinence from intercourse, blood revenge, and
warfare. Their effectiveness is implicit in calculations of the
consequences of uncontrolled reproduction. A four per cent rate
of increase would have created a population of 4-5 trillion in
5,570 years, half of the time since human colonization of the
lowlands (Cowgirl, 1975: 510; cf. Frank, 1987: 114). Both
ecological studies (Clark and Uhl, 1987; Fearnside, 1990) and
ethnographic evidence for environmental degradation following
forced sedentarism (Gross, 1983: 438) also indicate that the
densities of surviving unacculturated groups represent
sustainable carrying capacity.

Although formal and informal trade for commodities not locally
available has been characteristic of human groups since the Upper
Palaeolithic, the extensive networks of the neo-tropical lowlands
are peculiar in several respects. Items exchanged are often
necessities that could be manufactured locally, trading partners
must accept what is offered whether they desire it or not, and
hostile relations among the groups involved make participation
perilous (Chagnon, 1968; Coppens, 1971; Jackson, 1983: 99;
Mansutti R., 1986: 13-15; Meggers, 1971: 65; Oberg, 1953).
Several ethnographers have pointed out the role of these networks
in creating and perpetuating regional and ethnic interdependence
(Bodley, 1973: 595; Colson, 1985: 104; Coppens, 1971: 40). They
also serve as channels for transmitting all kinds of potentially
useful information among groups with different linguistic and
tribal affiliations and occupying different environments.

The similarities between prehistoric and recent settlement
behaviour (territoriality, impermanent residence, centripetal
village movement, site reoccupation, small homesteads) imply that
associated practices maximizing sustainable exploitation of
essential resources had evolved by the beginning of the Christian
era (when the adoption of pottery permits their recognition) and
probably earlier. The archaeological data provide no support for
the existence during preColumbian times of urban centres, highly
stratified sociopolitical or ganization, or expansive states.
Rather, they suggest a dispersed pattern of settlement by small
communities that were politically autonomous but socially and
economically interdependent.

During tens of thousands of years, the changing courses of
rivers and the fluctuations of climate divided and redivided the
landscape, segregating and reuniting populations of plants and
animals. Drift and natural selection enhanced divergence and
guided interactions, creating increasingly intricate
configurations that not only conserved the limited nutrients but
also moderated the range of variation in heat and humidity.
Arriving at the end of the Pleistocene, humans were the last of a
series of mammalian immigrants that entered via the Central
American passage and melted into the ecosystem. Like the rest of
the fauna, they returned in services as much as they took in
sustenance, sometimes knowingly, sometimes unaware.

Contemporary humans in the northern temperate zone came to
terms with a different set of edaphic, climatic, topographic, and
biotic conditions. Initially, their cultural development followed
a similar course. They too conserved resources and enhanced their
productivity. The motivation was the same: degradation meant
extinction. Slowly at first and then with increasing success,
some groups expanded their sustaining areas and their capacities
to transport commodities. By neutralising the immediate impact of
overexploitation, they were able to increase consumption while
degrading resources both locally (since deficits were compensated
by imports) and at a distance (since decimation in one location
could be compensated by moving to another).

During the past decade, the human sustaining area has become
synonymous with the surface of the planet. The scale of our
activities is now sufficient to alter the global climate, an
achievement equalled only once before in the history of the
earth. The blue-green algae that added oxygen to the atmosphere
eons ago and established the conditions for terrestrial life did
so unaware. Although we are conscious of our impact and its
potential consequences, we appear as helpless as the algae to
alter our behaviour. They survive inconspicuously today. Whether
humans will be so resilient is questionable.

Amazonia will play a critical role in the future of the
biosphere because of its influence on global climate. During the
past several millennia, the vegetation has suffered the
vicissitudes of repeated cli matic fluctuations and recovered.
Whether it will survive the impacts of accelerating human-induced
deforestation, erosion, and pollution seems less likely. The
pursuit of inappropoate policies will persist as long as
incentives and perceptions of alien origin remain dominant (Ledec
and Goodland, 1989: 448-51). Their continuing strength in spite
of negative economic, social, and environmental results bodes ill
for the future of the tropical forest and, if the climatologists
are correct, for the future of the biosphere as well.

The archaeological investigations undertaken under the
Programa Nacional de Pesquisas Arqueológicas na Bacia Amazônica
have been funded principally by the Neotropical Lowland Research
Program of the National Museum of Natural History, Smithsonian
Institution. I am grateful to the following colleagues for use of
their data: Bernardo Dougherty, Museo de La Plata, Argentina;
Ondemar F. Dias, Instituto de Arqueologia Brasileira, Rio de
Janeiro; Eurico Th. Miller, Eletronorte, Brasilia, and Celso
Perota, Universidade Federal do Espírito Santo, Vitôria. The
sequences on the lower Negro and Tocantins are based on the work
of Mario F. Simões, Museu Paraense Emílio Goeldi, Belém.

Carneiro, Robert (1978). "The knowledge and use of rain
forest trees by the Kuikuru Indians of central Brazil." In
The nature and status of ethnobotany (University of Michigan
Anthropological Papers 67), 201-16. Ann Arbor.

Ledec, George, and Robert Goodland. 1989. "Epilogue: An
environmental perspective on tropical land settlement." In
D.A. Schumann and W.L. Partridge (eds.), The human ecology of
tropical land settlement in Latin America (Westview, Boulder.),
435-67.

. 1994. "Archeological evidence for the impact of
mega-Niño events on Amazonia during the past two
millennia." Climatic Change 28: 1-18.

Meggers, Betty J., and Jacques Danon. 1988.
"Identification and implications of a hiatus in the
archeological sequence on Marajó Island, Brazil." Journal
of the Washington Academy of Sciences 78: 245-53.

Climatological studies on annual change in rainfall regimes in
South America were conducted by Ratisbona (1976) and Caviedes
(1981). Similar studies on the atmospheric circulation patterns
were conducted by Virji (1981). The rainfall regime of the
Brazilian Nordeste is divided into northern (north of 10°S) and
southern Nordeste by Hastenrath and Helter (1977). Markham and
McLain (1977), Moura and Shukla (1981), and Hastenrath (1984)
suggest a link between rainfall in the northern Nordeste and sea
surface temperature (hereafter called SST) anomalies in the
Atlantic Ocean. Walker (1928), Ramos (1976), Kousky and Chu
(1978), and Kousky (1979, 1985) studied the rainfall in the
Nordeste and atmospheric circulation over Brazil and the Atlantic
Ocean. The influence of the northern hemisphere circulation on
the rainfall in the Nordeste was investigated by Namias (1972).
Yamazaki and Rao (1977) studied the tropical cloudiness over the
South Atlantic Ocean.

A pilot study on annual change in tropospheric circulation and
its relationship to the monthly mean rainfall in South America
was conducted by Nishizawa and Tanaka (1983), as was a similar
survey on interannual change also by Tanaka and Nishizawa (1985).
Collec lively, these studies show a trough at the 150mb level
over the Nordeste which can be linked to regional subsidence and
to the relatively low amount of the rainfall in the Nordeste in
the drought year of 1983.

Empirical orthogonal function (EOF) analyses of rainfall in
Brazil on monthly, seasonal, and interannual time scales were
carried out by Tsuchiya et al. (1988) and Tanaka et al. (1988).
In addition, Aceituno (1988, 1989) analysed the rainfall and
atmospheric circulation associated with the Southern Oscillation.
These studies show that the inverse relationship between the
northern Nordeste and southern Brazil (hereafter called the NS
pattern), which appears in the First EOF, is best developed for
an interannual time scale of more than one year. The rainfall
difference between northern and southern Nordeste appears for all
time scales in the Second EOF. For the present study, the
relationship between the NS pattern and the Southern Oscillation
Index (SOI) is based on the normalized sea level pressure
difference between Tahiti and Darwin in the tropical Pacific
Ocean and the SST in the tropical Atlantic Ocean.

The source of the data for rainfall distribution and 850mb
height are from the Monthly Climatic Data for the World
published by the US National Oceanic and Atmospheric
Administration (NOAA) for the 10-year period from 1969 to 1978.
The data for EOF analysis (36 stations, 1968 to 1985) come from
the Superintendência do Desenvolvimento do Nordeste (SUDENE) for
the Nordeste region and from Boletim Agroclimatológico
published by the Agricultural Ministry of Brazil for the rest of
Brazil. Because locations of the rainfall data for the EOF
analysis are unevenly distributed, six of the locations shown are
the average of closely spaced stations. This averaging was
conducted because the EOF components can shift toward the area of
high concentration of the stations. Annual cycles in rainfall are
removed by subtracting the long-term mean (1968-85 average) for
each month of the year. The interannual component of rainfall
variability was extracted by filtering rainfall data by the
24-month triangular weighted running means (see Burroughs, 1978
for details). The triangular running means reduce short period
oscillations much more efficiently, compared to the simple
unweighted running means. However, about twice as many terms are
required compared to the simple running means. Hence, filtering
frequency below 12 months re quires about 24-month triangular
means. This filter was used because the regional variations in
the rainy season in Brazil are large. This means that the rainy
season is observed in certain regions in Brazil during any months
of the year. Hence it is difficult to define a cutoff month for
obtaining the annual totals. The EOF analysis of the anomaly
rainfall time series employed filtered data. Similar smoothing
was applied to the 850mb height and SST over the Atlantic Ocean.
Distribution of rainfall in South America and its relationship to
the tropospheric circulation are shown in detail by Nishizawa and
Tanaka (1983), as shown only by the examples for December (fig.
5.1) and April (fig. 5.2). In December, rainfall is especially
heavy in the Amazon Basin and the interior of Brazil. Because the
Intertropical Convergence Zone (ITCZ) over the Atlantic Ocean is
located north of the equator, dry areas are observed in the
Nordeste. In April, rainfall in the interior of Brazil begins to
decrease, while a southward dis placement of the ITCZ over the
Atlantic Ocean produces a brief rainy season in the Nordeste.

The interannual variability of rainfall in Brazil is analysed
by empirical EOF analysis for an 18-year period from 1968 to 1985
by using filtered data, as discussed previously.

The primary reasons for conducting EOF analysis are its
capability to reduce the dimensionality and to describe coherent
variability in the rainfall data. Since 27 locations are shown in
figure 5.3, there are 27 dimensions in the rainfall data. The EOF
analysis reduces the dimensions to few major components while
retaining the information contained in the original data. These
components are calculated to maximize the variance explained in
the original data. Hence, coherent variability in the original
data can be described by the first few components which contain
most of the variance. For these reasons, we believe that EOF
analysis depicts large-scale variability of the rainfall much
more clearly than the simple correlations between the 27
locations.

Figure 5.3 shows the distribution of the eigenvector of the
First EOF (24 M1) explaining 46.7 per cent of variance. The
pattern shows an inverse relationship in rainfall between
northern and southern Brazil (NS pattern). This pattern is
analysed by Aceituno (1988, 1989). The highest values are
concentrated near São Luiz and Fortaleza, where rainfall
variability is strongly influenced by the interannual variation
in intensity and location of ITCZ located near the equator.
Figure 5.4 shows the time coefficients for the First EOF.
Positive values in 1974 and 1985 show wet years in the northern
Nordeste. Negative values in 1972, 1976, and 1983 coincide with
dry years in northern Brazil and severe flooding in 1983 in
southern Brazil (see Tanaka and Nishizawa, 1985 for a detailed
case study).

Figure 5.5 shows the correlation of the 850mb height over
South America to the First EOF (24 M1). A region of high negative
correlation near Recife indicates a decrease (increase) in the
850mb height in wet (dry) years in northern Brazil. This pattern
shows intensification of the ITCZ in wet years in northern
Brazil.

Figure 5.6 shows the correlation of the smoothed Atlantic SST
to the First EOF (24 M1). High positive correlation values over
+0.8 are observed near 5-10°S, 15-10°W. The negative
correlation values over -0.4 are observed near 12°N, 40°W. This
SST dipole pattern was discovered by Hastenrath and Heller (1977)
and confirmed by Hastenrath (1978), and by Moura and Shukla
(1981). For 17 years of annual totals, the significant levels of
the correlations are 0.49 for the 5% level and 0.61 for the 1%
level. We believe that these values will be slightly higher for
the smoothed data.

Figure 5.7 shows the smoothed Atlantic SST at 5-10°S,
15-10°W. The wet years in northern Brazil of 1974 and 1985 (see
fig. 5.4) are the years with positive values of SST anomalies.
The dry years of 1972, 1976, and 1983 have negative values of SST
anomalies.

The relationship to SOI using normalised sea level pressure at
Tahiti and Darwin was investigated. Figure 5.8 shows the smoothed
SOI from 1967 to 1986. High positive values in 1974 and negative
values in 1972 and 1983 coincide with extreme rainfall in the
northern Nordeste (see fig. 5.4). This relationship is reversed
for the periods from 1969 to 1971 and from 1976 to 1978. Figure
5.9 shows the correlation of smoothed rainfall values (not EOF)
for 27 locations in Brazil compared to the smoothed SOI. The
correlation pattern is similar to the First EOF (24 M1) (see fig.
5.3). However, the regions with moderately high correlation over
0.4 are restricted to northern Brazil and to central and southern
Brazil. Figure 5.10 shows the correlation of the smoothed 850mb
height to the smoothed SOI. This pattern is very similar to
Hastenrath (1984). When this pattern is compared to the Atlantic
SST (fig. 5.5), it shows a high correlation to the subtropical
high near 20°S.

EOF analyses of monthly and seasonal (defined here as a
consecutive 4month period) variability of rainfall in Brazil show
the shorter timescale interaction between SST and rainfall. The
monthly EOF analysis of rainfall (Tanaka et al., 1988) reveals
rainfall distribution patterns of three distinct seasons.

Table 5.1 shows the variance explained by the first three
components of the seasonal and smoothed interannual rainfall (24
M). The First EOF in the December to March season is centred on
interior Brazil and has a component which shows a low
month-to-month persistence pattern. (Persistence is defined here
as the persistence from one month to the next month.) The low
persistence indicates that the monthly EOF pattern does not
persist in the next month. The First EOF (fig. 5.11) in the April
to July season is very similar to the First EOF (24 M1) of the
interannual time scale, which has a high month-to-month
persistence. The First EOF in August to November season is
centred on southern Brazil and has a low month-to-month
persistence.

Since the First EOF in April to July (4-7 M1) seasonal
rainfall has high month-to-month persistence and is very similar
to the NS pattern (24 M1) in interannual time-scale, correlation
to Atlantic SST was computed (see fig. 5.12). This pattern is
similar to the interannual time-scale (see fig. 5.6). An area of
negative correlation is located near 5-10°N, 45-40°W. This
resultant pattern is very similar to that of Moura and Shukla
(1981), who employed data from Fortaleza and Quixeramobim. Our
study shows that rainfall in northern Brazil is related to this
SST pattern.

Figure 5.13 shows the time change of the SST at 0-5°S,
15-10°W and the First EOF (4-7 M1) of seasonal rainfall. The
time changes of both parameters are very similar.

The rainfall in the semi-arid region has high interannual
variability. However, Nishizawa et al. (1986) have shown that
part of the subhumid northern coastal region in north-eastern
Brazil, with more than 1,000 mm of annual rainfall, has a high
(30-50 per cent) coefficient of variability in rainfall. Figure
5.14 shows annual rainfall variability in Brazil based on the 27
locations used in this study. As shown in the
lower part of this figure, most locations in Brazil show a
decrease in rainfall variability as the total rainfall increases.
However, Fortaleza and São Luiz show both greater variability
and annual rainfall, which indicates the unstable nature of the
climate at these locations. An inspection of other regions of
tropical climate shows that unstable rainfall of similar
magnitude (approximately over 1,000 mm per year) in relatively
humid locations is restricted to the regions directly influenced
by El Niño-Southern Oscillation (ENSO) in the equatorial Pacific
(e.g., Ocean Island and Tarawa) and coastal Ecuador (Guayaquil).

An interesting study on this topic was published recently by
Nicholls and Wang (1990), which showed that the annual rainfall
variability is typically higher for a specific mean rainfall in
areas affected by ENSO. In these areas of unstable climatic
regimes, any human development must consider careful water and
forest resource management in order to reduce the possible impact
of drought or floods caused by unusually wide fluctuations in
rainfall.

EOF analysis of interannual variability of rainfall in Brazil
confirmed an inverse relationship in the rainfall in the First
EOF between northern and southern Brazil (NS pattern), analysed
by Aceituno (1988, 1989). This pattern is best developed in
interannual and seasonal (April to July total) timescales. The
relationship between the NS pattern and the atmospheric
circulation pattern shows an intensification of the ITCZ in wet
years in northern Brazil. The correlation analysis of SOI and the
tropical Atlantic SST confirmed the earlier findings by
Hastenrath and Heller (1977) and Moura and Shukla (1981), that
the NS pattern is highly correlated (+0.80 to 0.86) to the SST
near 0-10°S, 15-10°W on the interannual and seasonal
timescales. Although detailed atmospheric circulation data over
the South Atlantic ocean are not available, weakening of the
trade winds in the South Atlantic is the probable cause of the
rise in SST in the equatorial South Atlantic. The negative
correlation in the SST near 5-10°N, 45-40°E suggests that
southward migration in South America of the ITCZ coincides with
the increase in rainfall in northern Brazil. The influence of the
Southern Oscillation is found to be less than Atlantic SST.
However, the extreme cold event in 1974 (wet year in northern
Brazil) and the warm event in 1983 (dry year) coincided with
rainfall extremes of the NS pattern.

The EOF analysis of the seasonal variability of rainfall in
Brazil have shown that the First EOF in the December to March
season is centred on interior Brazil and has a low month-to-month
persistence pattern. The First EOF in August to November season
is centred on southern Brazil and has a low month-to-month
persistence.